For example, there is proposed a so-called color image forming apparatus, in which a photosensitive unit including a plurality of photosensitive members, chargers charging the photosensitive members, developing rollers feeding developing agents to the photosensitive members and cleaning brushes capturing foreign matter adhering to the photosensitive members in response to the colors of the developing agents, is detachably mounted.
In the image forming apparatus, wire electrodes applying biases to discharge wires of the chargers, grid electrodes applying biases to grids of the chargers, developing roller electrodes applying biases to the developing rollers and cleaning electrodes applying biases to the cleaning brushes are provided on the same side surface of a drum unit as the photosensitive unit in response to the colors respectively. These electrodes come into contact with contacts individually provided on the main body of the image forming apparatus when the drum unit is mounted in the main body of the apparatus, to be fed with power from the main body of the apparatus.
Among these electrodes, the wire electrodes and the cleaning electrodes are arranged on the same straight line extending along a direction for mounting or dismounting the photosensitive unit in or from the main body of the apparatus, while the grid electrodes and the developing roller electrodes are arranged on the same straight line extending along the direction for mounting or dismounting the photosensitive unit in or from the main body of the apparatus, to form a train parallel to a train of the wire electrodes and the cleaning electrodes at an interval.
In the photosensitive unit, the intervals between the adjacent electrodes must be generally increased, in order to reliably bring the electrodes and the corresponding contacts provided on the main body of the apparatus into contact with one another and to prevent an electric leak between the electrodes. In particular, the interval between the train of the wire electrodes and the cleaning electrodes and the train of the grid electrodes and the developing roller electrodes must be increased. In this case, however, the degree of freedom in design may be reduced.